Automated on-line capacity expansion method for storage device

ABSTRACT

A volume provider unit in a computer system that detects a logical block address of a read or write I/O accessing a logical volume of a storage device from a host. According to the logical block address fetched, a storage domain of the logical volume is dynamically expanded. Moreover, the storage domain of the logical volume is reduced or expanded according to an instruction of logical volume capacity reduction or expansion from a host commander part to a volume server.

CROSS-REFERENCES

This application is a continuation application of U.S. patentapplication Ser. No. 12/245,122, filed Oct. 3, 2008, which is acontinuation of U.S. patent application Ser. No. 10/991,421, filed Nov.19, 2004 (now U.S. Pat. No. 7,447,832), which is a continuation of U.S.patent application Ser. No. 10/782,787, filed Feb. 23, 2004 (now U.S.Pat. No. 6,836,819), which is a continuation of U.S. patent applicationSer. No. 09/931,253, filed Aug. 17, 2001 (now U.S. Pat. No. 6,725,328),the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for successive capacityexpansion during on-line operation in a storage device system.

2. Description of the Related Art

Recently, storage domains of a plurality of host computers are oftenstored in a single storage device. This tendency is promoted by, forexample, a disk array. The disk array provides redundancy of the storagedomains by a plurality of magnetic disk devices in a system, therebyincreasing reliability and providing a necessary storage domain as alogical volume to a plurality of hosts. One of the merits of using thisdisk array is capacity expansion of the logical volume.

For example, when a computer has used up a logical volume provided by adisk array, a free space in the disk array is cut out with an arbitrarylength to be allocated as a logical volume, so that the computer canconnect this logical volume to a logical volume in use, therebyexpanding the storage domain. This function of volume expansion can alsobe performed during on-line and is called on-line volume expansion. Theon-line volume expansion enables to expand a range of the logical volumestorage domain corresponding to data increasing as time passes, withoutstopping the application and accordingly, enables to expand theapplication operation time. Moreover, upon volume capacity transfer,there is no need of data transfer between volumes, which significantlyreduces the storage management cost.

Conventionally, a logical volume user should report to a logical volumeprovider when expanding the on-line volume. In a small-size site such aswithin a single enterprise, there is no sudden data increase and it isnot necessary to perform on-line volume expansion all the time. However,in a large-size site such as a data center where a plurality ofenterprises utilize data, there is a possibility of a sudden dataincrease from computers of the plurality of enterprises and it isnecessary to perform the on-line volume expansion at all time. Moreover,in order to enhance the utilization effect of a storage domain of a diskarray or the like, it is necessary to provide a volume to a plurality ofusers in a single storage device without waste.

In order to effectively use a storage domain in a storage device, it isnecessary to manage the storage area in unit of a logical volume of asmall capacity and to expand the logical volume with the small-capacitylogical volume when required. When using the on-line volume expansion inthis condition, there is a case that a request for the on-line volumeexpansion is simultaneously caused by a plurality of users due to thedata increasing as time passes and the logical volume provider may notbe able to satisfy the requests. In the worst case, the on-line volumeexpansion cannot be performed and the computer operation is stopped.

A logical volume user make a request for an unlimited storage capacitywithout managing the storage domain. On the other hand, the logicalvolume provider should effectively manage the storage domain so as toprovide a logical volume to the user as rapidly as possible withoutconsidering how the storage domain is used by the logical volume user.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to solve the requestsof the storage resource user and provider by using a storage domainmanagement apparatus capable of dynamically allocating a storage domainof an appropriate capacity from the storage domain collectively managedduring a computer on-line operation, thereby expanding the logicalvolume.

A computer system according to the present invention includes at leastone host computer, at least one disk device, and a volume providingdevice which are connected to one another. The volume providing devicemanaging a plurality of disk devices provides a logical volumecorresponding to each of the host computers from the plurality of diskdevices. The host computer sends an I/O request to a logical volume, anda volume providing part interprets a logical block address where the I/Orequest is read and written. When the logical volume has no storagedomain of the logical block address accessed by the I/O request, thevolume providing device allocates a storage domain from a free magneticdisk device, thereby dynamically expanding the logical volume storagedomain. Moreover, the logical volume is reduced by an arbitrary amountindicated by an application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows configuration of a storage device system;

FIG. 2 shows a segment management table 2000;

FIG. 3 shows a physical and logical management table 3000;

FIG. 4 shows a physical relationship between LUN0 (4000), segment 1(3410), segment 2 (3420), and segment 3 (3430);

FIG. 5 shows a flow of an I/O operation performed between a host 1100and a volume server 1200;

FIG. 6 shows an operation flow of an I/O detector part 1231;

FIG. 7 shows an operation flow of a capacity controller part 1232;

FIG. 8 shows an operation flow of a volume expansion process between asegment manager part 1233, the capacity controller part 1232, andphysical and logical address manager 1235;

FIG. 9 shows an operation of a volume reduction process between thesegment manager part 1233, the capacity controller part 1232, and thephysical and logical address manager 1235;

FIG. 10 shows an operation flow of segment state management by thesegment manager part 1233;

FIG. 11 shows an operation flow of disk addition or deletion by thesegment manager part 1233;

FIG. 12 shows an operation flow of an I/O processor part 1234;

FIG. 13 shows an operation from of a physical and logical addressconversion by the physical and logical address manager 1235;

FIG. 14 shows a logical relationship between the LUN 14000, segment14201, the segment 14202, and a magnetic disk device 14100;

FIG. 15 shows an operation flow of addition/deletion of a segmentto/from the physical and logical management table by the physical andlogical address manager 1235;

FIG. 16 shows an operation flow of a logical volume storage capacityexpansion between a commander part 1132 in the host 1100 and thecapacity controller part 1232 in the volume server 1200;

FIG. 17 shows a physical format of an I/O command; and

FIG. 18 shows an operation flow of a logical volume storage capacityexpansion between the commander part 1132 in the host 1100 and thecapacity controller part 1232 in the volume server 1200.

DESCRIPTION OF THE EMBODIMENTS

Description will now be directed to embodiments of the present inventionwith reference to the attached drawings.

(1) First Embodiment

FIG. 1 shows a configuration m system includes a plurality of hosts1100, a volume server 1200, and a plurality of magnetic disk device1300. In this embodiment a single host 1100 and three magnetic diskdevices are used, but only one magnetic disc device or any numbers ofdevices 1300 may be used instead. Moreover, the host 1100, the volumeserver 1200, and the magnetic disk devices 1300 have CPU, memory, andthe like but they are not direction relationship with explanation of theembodiment of the present invention and their explanations are omitted.

The host 1100 has an application program (App) 1110, an operating system(hereinafter, referred to as OS) 1130, and a channel interface 1140. Theapplication 1110 is application software such as a DB and a file systemfor reading and writing from/to a volume provided from the volume server1200 as the volume providing device. The operating system 1130 includesa volume device part (rsd0) 1131 for receiving an I/O request from theapplication 1110 and transferring the I/O request to the channelinterface (I/F) 1140, and a commander part 1132. The commander part 1132is software performing management of logical area information includinga start block position and an end block position of the storage deviceused by the OS 1130 and operation control of the volume server 1200.

By referring to FIG. 4 showing a logical volume as a storage domainprovided by the volume server 1200, explanation will be given on thelogical area information 4100. Since in this embodiment a volume isdynamically expanded, the start block position of the logical areainformation handled by the OS 1130 is indicated by OLBA (4200) and theend block position indicates a capacity of the maximum storage devicesupported by the OS of the storage device or a storage capacity used bya user. When the maximum capacity is limited by a storage capacity usedby the user, the storage domain of the logical volume provided by thevolume server 1200 is also limited by this end block position. Moreover,the logical area information is stored in the storage device managed bythe OS 1130 in a necessary area between the start block position OLBA(4200) and LBA to define the necessary area (4100). Normal data to bestored is stored in a storage domain (4400) other than the logical areainformation.

The I/F 1140 shown in FIG. 1 is a block device I/F having a function totransfer an I/O from the OS 1130 to an external device such as a fibrechannel I/F and an SCSI I/F.

A command controlling between the host 1100 and the volume server 1200and between the volume server 1200 and the magnetic disk device 1300 iscalled an I/O request. The I/O request is a command of a block deviceprotocol such as the SCSI protocol. FIG. 17 shows a command format ofthe I/O request. The I/O request has an operation code 17001, a LUN(logical unit number) 17002, an LBA (logical block address) 17003, and atransfer data length 17004. The operation code 17001 is a numberindicating a read process, write process, and the like. The LUN 17002 isa unique number of a logical volume to be processed by the command. TheLBA 17003 is a position for processing a logical volume provided by thevolume server. The transfer data length 17004 shows an amount to beprocessed all-at-once by the I/O request.

The volume server 1200 includes: a channel I/F 1210 at the host side; avolume provider part 1230 performing processing of an I/O requestrequested from the host 1100 and management of the magnetic disk device1300; and a channel I/F 1220 for transferring the I/O request requestedby the volume provider part 1230 to the magnetic disk device 1300. Thechannel I/F 1200 at the host side is a block device I/F such as a fibrechannel I/F and the SCSI which can be connected to the host 1100. Inthis embodiment, the channel of the host 1100 side is separated from thechannel of the magnetic disk device 1300 side but the channel I/F 1210of the host 1100 side and the channel I/F 1220 of the magnetic diskdevice 1300 may be shared by each other.

Moreover, this volume server 1200 provides a logical volume having alimitless capacity to the host 1100. That is, when the volume server1200 is viewed from the host 1100, the start value of the logical blocknumber (LBA) defining a volume range is always 0 but the LBA of therange end may not be determined. Moreover, when the LBA of the range endis defined, the value indicates the volume maximum capacity provided bythe volume server 1200.

The volume provider part 1230 in the volume server 1200 includes an I/Odetector part 1231, a capacity controller part 1232, a segment managerpart 1233, and I/O processor part 1234, and a physical and logicaladdress manager 1235. The segment manger part 1233 has a segmentmanagement table 2000 inside, and this segment management table 2000 isused to perform management of the storage domain of the volume providedby the volume server 1200.

The segment management table 2000 shown in FIG. 2 includes a disk number(disk ID) 2100, a segment number (Segment Number) 2200, a starting LBA(LBA (START)) 2300, a segment size (Size) 2400, and a value of segmentstate (In-Use) 2500. The disk ID 2100 is a unique identification numberof a disk determined by a block level protocol such as the SCSI when themagnetic disk device 1300 is connected to the volume server 1200. Thesegment is a minimum unit of a storage domain in each of the magneticdisk device 1300 to be managed by the volume server 1200, and thesegment number 2200 is a unique identification number for management ofthe segment by the volume server 1200. The LBA (START) 2300 defines aphysical position where the storage domain of the segment starts in themagnetic disk device 1300 of the disk ID 2100. The segment sizeindicates the storage domain starting at the LBA (START) 2300 in thedisk. The segment state indicates whether the segment storage domain isused or not used by the volume server 1200, using two values: value 1indicates the in-use state and value 0 indicates the not-in-use state.

Next, the physical and logical address manager 1235 performs physicaland logical management between a logical volume provided by the volumeserver 1200 and the magnetic disk device 1300 storing data. As means formanaging the logical volume and the magnetic disk device 1300 containingreal data, the physical and logical address manager 1235 has a physicaland logical management table 3000 of FIG. 3. This physical and logicalmanagement table 3000 is used for management of a logical unit number(LUN) 3100, a segment number (Segment Number) 3200, a LUN LBA (START)3330, and a LUN LBA (END) 3400. The LUN 3100 is called a logical unitnumber indicating a unique number of a logical volume provided from thevolume server 1200 to the host 1100. The segment number 3200 is a uniquenumber of a storage domain managed by the segment manager part 1233. Alogical volume provided by the LUN 3100 consists of a plurality ofsegments and the logical block numbers (LBA) of the logical volume aresuccessively connected in an ascending order (from younger to older) ineach LUN 3100 of the physical and logical management table 3000.

For example, in FIG. 3, when LUN0 (3500), the segment number 1 (3510),the segment number 2 (3520), and the segment number 3 (3530) areconnected in this order and are provided, as shown in FIG. 4, as asingle logical volume of the LUN0 (4000) to the host 1100. The LUN LBA(START) 3300 indicates a start position of the LBA used by the segmentin the LUN. The LUN LBA (END) 3400 indicates an end position of the LBAused by the segment in the LUN. The I/O detector part 1231 detects LBAin each I/O request accessed from the host 1100 to the magnetic diskdevice 1300. The I/O processor part 1234 performs I/O processing ofactual read/write. The capacity controller part 1232 increases/decreasesa capacity requested from the I/O detector part 1231 or the commanderpart 1132 of the host 1100.

In this embodiment, the volume server 1200 is arranged as an independentunit but it is also possible that the magnetic disk device 1300 has thefunction of the volume server 1200.

Moreover, in this embodiment the volume expansion is performed insegment basis but the volume expansion can also be performed in blockbasis as follows. When the segment manager part 1233 and the physicaland logical address manager 1235 are considered to be, for example, acapacity-expandable file system such as a Log Structured file system,the segment as the minimum unit of the storage domain in the segmentmanagement table 2000 and in the physical and logical management table3000 can be replaced by a block which is the minimum unit of the filesystem storage domain and the file of the file system can be consideredto be a logical volume having the LUN 3100 provided from the volumeserver 1200. That is, even when the segment manager part 1233 and thephysical and logical address manager 1235 are replaced by a file system,it is possible to provide a logical volume which can be dynamicallyexpanded in block basis.

Next, explanation will be given on the operation of the volume server1200, referring to FIG. 5. After an I/O request is issued from the host1100 to the volume server 1200 (step 5001), the volume server 1200performs processing of the received I/O request in the volume providerpart 1230 (step 5002). Upon completion of the I/O request processing, anI/O request processing completion report is issued to the host 1100(step 5003). The host received the I/O completion report (step 5004) andthe process is terminated. The volume provider part 1230 of the volumeserver 1200 seems to operate in the same way as a controller of aconventional magnetic disk device 1300 but it is configured to be ableto expand a volume without limit. Hereinafter, explanation will be givenon the internal operation of the volume provider part 1230 having thisconfiguration.

The volume provider part 1230 is operated by combination of the I/Odetector part 1231, the I/O processor part 1234, the physical andlogical address manager 1235, the capacity controller part 1232, and thesegment manger part 1233. In an enlarged view 1236 of the volumeprovider part 1230 of FIG. 1, thick lines indicate an I/O request flowand thin lines indicate a control flow. Firstly, an I/O request flowingfrom the host side I/F 1210 is processed by the I/O detector part 1231and then LBA of each I/O request is physically-logically converted inthe I/O processor part 1234, after which read or write is performed fromor to the respective magnetic disk devices 1300. This processing flowwill be detailed below.

Firstly, explanation will be given on the operation of the I/O detectorpart 1231, referring to FIG. 6. A currently allocated domain capacity ofa logical volume in each LUN is calculated by adding the respectivesegment size 2400 in the LUN using the segment number of the physicaland logical management table 3000 of FIG. 3 and the segment managementtable 2000 of FIG. 2 describing the size 2400 of each segment (step6001). When an I/O request is sent from the host 1100, an LBA to beaccessed in the logical volume by the I/O request is detected (step6002). When the currently allocated area is determined to be larger thanthe LBA accessed (step 6003), the I/O processing is requested to thephysical and logical address manager 1235 (step 6005). When thecurrently allocated area is determined to be smaller than the LBAaccessed (step 6003), then a capacity allocation is requested to thecapacity controller part 1232 (step 6004) and the I/O processing isrequested to the I/O processor part 1234 (step 6005).

Next, referring to FIG. 7, explanation will be given on the operation ofthe capacity controller part 1232. The operation is different for arequest from the I/O detector part 1231 and for a request from thecommander part 1132 of the host 1100. Firstly, explanation will be givenon the operation for the I/O detector part 1231. When the I/O detectorpart 1231 issues a capacity increase command (step 7001), a volumeincrease processing is performed (step 7002) and the processing isterminated. On the other hand, when the commander part 1132 of the host1100 issues a command to reduce the entire capacity by mLBA (step 7001),the volume reduction by mLBA is performed (step 7003).

In a volume increase processing (step 7002), the segment manager part1233 operates in combination with the physical and logical addressmanager 1235 as follows (FIG. 8). Firstly, a free segment fetch requestis sent to the segment manager part 1233 with a segment number parameterSN=−1 (step 8001). When the segment requested is present, the segmentmanager part 1233 puts a segment number (SN>=0) in the segment numberparameter SN and returns it. When the segment requested is not found,SN=−1 is returned (step 8002). Upon reception of the segment number, thecapacity controller part 1232 determines whether the segment numberparameter SN is a positive number (step 8003). If SN>=0, the process iscontinued and if SN<0, an error is returned (step 8006), thusterminating the process. The capacity controller part 1232 makes avolume connection request to the physical and logical address manager1235 according to the segment number SN fetched from the segment managerpart 1233 (step 8004). The physical and logical address manager 1235,according to the segment number, connects a segment to the end segmentof a logical volume as a target LUN in the physical and logicalmanagement table 3000 (step 8005), thus terminating the process. Theoperation of this physical and logical address manager 1235 will bedetailed later.

On the other hand, a volume reduction process (step 7003) is performedas follows (FIG. 9). When the reduction capacity is mLBA, at least onesegment number having no logical volume domain after the reduction isfetched from the physical and logical management table 3000 (step 9001).The segment fetch is performed as follows. Firstly, from the physicaland logical management table 3000, the LBA after the reduction iscalculated from the end LBA (3400) as LBA (END)−m. According to this LBAafter the reduction, one or a plurality of segment numbers (SN) notoverlapping with the LBA after the reduction in the target LUN arefetched.

Next, for these segments, a segment return request is made to thephysical and logical address manager 1235 (step 9002). The physical andlogical address manager 1235 disconnects a record matched with thesegment number (SN 3200, LBA (START) 3300, LBA (END) 3400) from the listof the logical volume specified by the LUN in the physical and logicalmanagement table 3000 (step 9003). The capacity controller part 1232issues a command to manage the disconnected segment number SN as a freesegment to the segment manager part 1233 (step 9004). The segmentmanager part 1233 manages the disconnected segment as a free segment(step 9005). The disconnection of the logical volume is reported to thehost 1100 (step 9006). Thus, the volume reduction process is completed.

The segment manager part 1233, upon reception of an instruction from thecapacity controller part 1232, performs a segment state management ofthe segments described in the segment management table 2000 andmanagement of segment addition/deletion. The segment state management isperformed according to the aforementioned management procedure of thesegment management table 2000.

Referring to FIG. 10, explanation will be given on the operation of thesegment state management. Firstly, a volume control request is passedfrom the capacity controller part 1232 together with a segment number ofan argument. If the segment number <0, it is determined that the requestis made for fetching a free segment (step 10001) and the processproceeds to step 10002. When the free segment fetch request is made, itis checked whether a free volume exists by using the segment managementtable (step 10002). If no volume is free (step 10002), an error isreported to the capacity controller part 1232 (step 10005). If a freesegment exists (step 10002), the segment number of the free segment isreturned to the capacity controller part 1232 (step 10003). The statefor the segment in the segment management table is modified to 1indicating the in-use state (step 10004) and the process proceeds tostep 10007.

On the other hand, if the segment number >=0 (step 10001), the requestis determined to be an operation for transferring the segment not-in-usestate, and the process is continued in step 10006. In step 10006, thestate of the segment number is set to 0 indicating the not-in-use statein the segment management table 2000 and the process proceeds to step10007. In step 10007, by using items of the state 2400 in the segmentmanagement table 2000, a segment use ratio (the number of segments inuse against the total number of segments) is calculated from the numberof segments in use and the total number of segments and it is determinedwhether the use ratio is equal to or more than 90%. If the use ratio is90% or above, a request is made to a maintenance staff to add a magneticdisk device 1300 (step 10008), thus terminating the process. If the useratio is below 90%, then the process is terminated as it is. Thethreshold value of the use ratio may also be set to other than 90%according to the system reliability by the maintenance staff. Thiscompletes the explanation on the operation of the volume use statemanagement by the segment manager part 1233.

Next, referring to FIG. 11, explanation will be given on theaddition/deletion operation of the magnetic disk device 1300. Step 11001determines whether a volume addition or deletion is to be performed. Ifaddition, then the process proceeds to step 11005; and if deletion, theprocess proceeds to step 11002. In case of addition of the magnetic diskdrive 1300, step 11005 checks the capacity of the magnetic disc device1300 (step 11005). According to the capacity checked, the number ofsegments and the size are determined (step 11006). The number ofsegments and the size may be values specified by a maintenance staff orfixed values According to the values, upon each addition of a magneticdisc drive 1300 to the end of the segment management table 2000, thedisk ID 2100, the segment number 2200, the start position 2300, thesegment size 2400, and 0 (not-in-use) as the use state 2500 are inserted(step 11007), thus completing the process.

On the other hand, in case of a volume deletion, it is determined thatthe segment of the segment number is a free segment or not (step 11002).If the segment is free, a record of that segment number is deleted fromthe segment management table 2000 (step 11003). If the segment is not afree segment (step 11002), an error is returned and the process isterminated (step 11004).

This completes the explanation on the segment addition/deletionoperation of the segment manager part 1233. The segment manager part1233 performs management of the segment use state and theaddition/deletion operation according to the aforementioned procedure.

Referring to FIG. 12, explanation will be given on the operation of theI/O processor part 1234. Firstly, an I/O request sent from the I/Odetector part 1231 to the I/O processor part 1234 requests the physicaland logical address manager 1235 to convert the LBA of the I/O requestinto a physical address (step 12001). Next, a type of the I/O request isdetermined (step 12002). If the I/O request is a read I/O, using thephysical address, data is read out from the magnetic disk device 1300(step 12003) and the read out data is returned to the host 1100 (step12004). If the I/O request is a write I/O, using the physical address,data is written to the magnetic disk device 1300 (step 12005) and thewrite completion is reported to the host 1100 (step 12006). Thiscompletes the explanation on the operation procedure of the I/Oprocessor part 1234.

The operation of the physical and logical address manager 1235 can beseparated in two processes. One of them is a physical and logicaladdress conversion procedure requested by the I/O processor part 1234.This conversion procedure will be explained with reference to FIG. 13and then a physical-logical structure between an actual physical addressand a logical address will be explained with reference to FIG. 14. Forthe conversion, a rule as follows is used. Firstly, a segment groupcorresponding to the LUN as an I/O request target is selected (step13001). A disk number and an LBA of the physical side are calculatedfrom the LBA (step 13002).

The calculation is performed as follows. Firstly, according to an LBAtarget described in the I/O request, by referencing each segment startLBA from the physical and logical management table 3000, segment number(SN) to be accessed by the LBA target (143000 in FIG. 14) is selectedfrom a plurality of segments to which the target LUN belongs. Accordingto the selected segment number SN, using the segment management table2000, a disk ID to be accessed by the LBA target (14300), and a physicaladdress of the segment from the head of the magnetic disk device arespecified. When viewed from the N-th segment head physical address LBAN(14003), the address on the segment where data is operated is LBAtarget−LBAN. Accordingly, the physical address of the segment from thehead of the magnetic disk device 1300 is: (segment head LBA LBAsegstart)+(LBA target−LBAN) (14005). The disk ID 2100 and the value of(segment head LBA LBA segstart)+(LBA target−LBAN) (14005) as the LBA ofthe magnetic disk device 1300 of the disk ID 2100 are returned to theI/O processor part 1234 (step 13003).

The other operation process of the physical and logical address manager1235 is volume addition/deletion to/from the physical and logicalmanagement table 3000. This operation will be explained with referenceto FIG. 15. A LUN in the physical and logical management table isselected (step 15001). For a volume addition (step 15002), a segmentnumber to be added is given from the capacity controller part 1232 andin the LUN volume to be added, the segment is added to the end of thesegment record (step 15003). Here, when the added segment is viewed fromthe host 1100, an added volume exists between the addresses from LBAN(14003) to LBAN+SIZEN (14004). When deleting a volume (step 15002),after receiving an instruction of deleting mLBA from the capacitycontroller part 1232, the capacity of mLBA is deleted in segment basisfrom the end of the segment record in the LUN volume to be deleted (step15004). The segment deleted returns its segment number to the capacitycontroller part 1232 (step 15005). This completes the explanation of theoperation of the physical and logical address manager 1235.

The commander part 1132 of the host 1100 is a program which, afterreducing the data capacity in the volume used by the application 1110,upon reception of an instruction from the application or the user, sendsan instruction to the volume server 1200 via the I/F 1140 so as toreduce in segment basis the storage domain of the logical volumeprovided by the volume server 1200. This operation will be detailedbelow by referring to FIG. 16.

Firstly, a request to reduce the volume by mLBA is received from theapplication 1110 (step 16001). The commander part 1132 reduces by mLBAthe end block position of the logical area information of the logicalvolume under control of OS 1130 (step 16002). The volume of mLBAcapacity is issued from the commander part 1132 to the capacitycontroller part 1232 of the volume server (step 16003). The capacitycontroller part 1232 performs a volume reduction processing (step 16004)and returns the result to the host 1100. This completes the explanationof the operation of the commander part 1132.

Next, explanation will be given on the interlocked operation with theapplication 1110. As has been described above, the host 1100 can handlea logical volume provided from the volume server 1200 as an existingvolume. However, when a volume exceeding the segment held by the volumeindicated by the LUN is accessed in the volume server 1200, a volume isadded from the segment manager part 1233. This operation is identical tothe operation of the aforementioned volume provider part 1230.

On the other hand, when the application 1110 has performed a volumecapacity control of a volume expanded by itself and the capacityactually used by the application 1110 has reduced, a capacity differencebefore and after the deletion is reported to the commander part 1132 ofthe host 1100 by the application 1110 and the aforementioned volumereduction procedure (FIG. 16) is performed in the volume server via thecommander part 1132 of the host 1100. By these processes, the number ofsegments in use by the volume server is matched with the operation ofthe application 1110 and an appropriate logical volume capacity can beprovided.

(2) Second Embodiment

In the first embodiment, when a write I/O access occurs to other than astorage domain of a logical volume provided from the volume server 1300to the host 1100, the volume server 1200 successively allocates astorage domain, thereby performing a storage domain expansion to thelogical volume provided by the volume server 1200. In the secondembodiment, according to an instruction of the application 1110, astorage capacity expansion of a logical volume is performed in advancevia the commander part 1132 of the host 1100 and the storage capacity ofthe logical volume is recognized by the OS 1130 before becoming usableby the application 1110. This procedure will be explained by referringto FIG. 18.

Firstly, the commander part 1132 of the host 1100 receives a storagedomain expansion request by mLBA from the application 1110 (step 18001).The commander part 1132 of the host 1100 issues a write I/O to the LBAas a total of the entire logical volume capacity and the expanded domainmLBA (step 18002). The I/O detector part 1231 of the volume server 1200performs a capacity expansion processing to the capacity controller part1232 because the volume provided by the volume server is expanded bymLBA (step 18003). If the write I/O is successful (step 18004) and thestorage domain is increased, then step 18005 is performed, and if thewrite I/O fails, the process terminates without performing the storagedomain expansion. In step 18005, the commander part 1132 of the host1100 increases by mLBA the end block count of the logical areainformation of the OS 1130 corresponding to the logical volume providedby the volume server 1200. This completes the explanation of the storagedomain expansion procedure of the logical volume provided from thevolume server 1200 via the application 1110.

According to the present invention, by adding a storage domain to avolume server according to a request from the volume server, theapplication of the host computer can use a single volume which can bedynamically expanded.

1. A control method in a storage system including a plurality of disk devices, the method comprising the steps of: managing a plurality of storage areas provided from the plurality of disk devices; providing a plurality of logical volumes, receiving an instruction to expand a capacity of at least one of the plurality of logical volumes, expanding the capacity of the at least one of the plurality of logical volumes, and monitoring a capacity of storage areas allocated to the plurality of logical volumes relative to a capacity of the plurality of storage areas, wherein, in response to a write request to one of said plurality of logical volumes, at least one of the plurality of storage areas can be allocated thereto.
 2. The control method according to claim 1, further comprising the step of: allocating the at least one of the plurality of storage areas to a portion of said one of the plurality of logical volumes, if the at least one of the plurality of storage areas is needed in order to write data of the write request and is not allocated to the portion of the one of the plurality of logical volumes.
 3. The control method according to claim 1, further comprising the step of: writing data of the write request to the at least one of the plurality of storage areas, after the at least one of the plurality of storage areas is allocated.
 4. The control method according to claim 1, further comprising the step of: in response to another write request addressed to a portion of said one of the plurality of logical volumes to which the at least one of the plurality of storage areas is allocated, after receiving the write request, updating data on the at least one of the plurality of storage areas by data of the another write request.
 5. The control method according to claim 1, wherein: the plurality of storage areas are a plurality of segments.
 6. The control method according to claim 1, further comprising the step of: if a value obtained by the monitoring step is equal to or greater than a threshold, requesting at least one additional disk device to be add to the plurality of storage areas so as to increase the capacity of the plurality of storage areas.
 7. The control method according to claim 1, further comprising the step of: if a ratio calculated based on the monitoring step is equal to or greater than 90%, requesting at least one additional disk device. 